Migration imaging method employing a uniform exposure step

ABSTRACT

A method of imaging which comprises providing an imaging structure having a support, an overlayer of softenable material containing a particulate photosensitive material, forming a latent image on said structure, developing said latent image whereby an image is formed by the selective migration of photosensitive particles in image configuration, and terminating said migration by uniform exposure to activating radiation at a time subsequent to the beginning of said developing step.

[ MIGRATION IMAGING METHOD EMPLOYING A UNIFORM EXPOSURE STEP [75] Inventor: William L. Goffe, Webster, NY.

{73] Assignee: Xerox Corporation, Stamford,

Conn.

[221 Filed: Jan.28, 1974 211 Appl.No.:437,266

Related US. Application Data [63] Continuation of Ser. No. 695,238. Jan. 2, l968.

abandoned,

[52] US. Cl. 96/1 PS; 346/74 ES [51] Int. Cl. G03G 13/22 [58] Field of Search 96/l PS, l PE, 1 R

[56] References Cited UNITED STATES PATENTS 2,990.2 79 6/196] Crumley et al. 96/L8 3.238.041 3/1966 Corrsin t t 96/l.l 3.5 l5.549 6/1970 Bixby t t i. 96/l.5 3.648.607 3/l972 Gundloch 96/l PS X Nov. 11, 1975 3.653.885 4/l972 Levy et al 96/l PS 3.713.8l8 H1973 Gaffe 3.795.512 3/1974 Knieser 96/l PS 3,80l.3l4 4/l974 Goffe 96/l PS 3.836.362 9/1974 Goffe 96/] PS 3,839,030 l(l/l974 Goffe 96/l R Primer Examiner-Roland E. Martin, Jr. Assistant Examiner-John R. Miller [57] ABSTRACT A method of imaging which comprises providing an imaging structure having a support. an overlayer of softenable material containing a particulate photosensitive material. forming a latent image on said structure, developing said latent image whereby an image is formed by the selective migration of photosensitive particles in image configuration, and terminating said migration by uniform exposure to activating radiation at a time subsequent to the beginning of said developing step.

11 Claims, 6 Drawing Figures US Patent Nov. 11, 1975 3,918,969

1:; J f L I /l L0 F/6.5 L mi l3 O O O O fl? INVENTOR F/G.6 L WILLIAM L. 0011-1: Quv-vflfikyow A 7' TORNEKS MIGRATION IMAGING METHOD EMPLOYING A UNIFORM EXPOSURE STEP CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation ofcopending application Ser. No. 695,238, filed Jan. 2, I968 now abandoned.

BACKGROUND OF THE INVENTION This invention relates in general to imaging, and more specifically, to an improved imaging system.

There has been recently developed a migration imaging system capable of producing high quality images of high density, continuous tone, and high resolution. This system is described and claimed in copending applica tion Ser. No. 403,002, filed Oct. l2, I964, now abandoned and other related copending applications. In a typical embodiment of this imaging system, an imaging structure comprising a conducting substrate with a layer of softenable or soluble plastic material, containing photosensitive particles overlaying the conductive substrate is imaged in the following manner: An electrostatic latent image is formed on the photosensitive surface, e.g., by uniform electrostatic charging and exposure to a pattern of activating electromagnetic radiation. The softenable layer is then developed by exposing the plate to a solvent which dissolves only the soluble layer. The photosensitive particles which have been exposed to radiation migrate through the softenable layer as it is softened and dissolved, leaving an image on the conductive substrate conforming to a negative of the original. This is known as a positive-to-negative image. Through the use of various techniques, either positive-to-positive or positive-to-negative images may be made depending on the materials used and the charging polarities. Those portions of the photosensitive layer which do not migrate to the conductive substrate may be washed away by the solvent with the softenable layer.

In another embodiment, a migration image is formed by exposing the structure defined above to a solvent vapor to form a migration image composed of photosensitive particles selectively dispersed in depth within the softenable plastic.

The migration imaging process comprises a com bination of process steps which usually include charging, exposing, and developing with a solvent or by heat. The characteristics of these images are dependent on such process steps as potential, exposure, and development, as well as the particular combination of process steps. High density, continuous tone and high resolution are some of the photographic characteristics possible. The image is characterized as a fixed or unfixed photosensitive particle image which can be used in a number of applications such as microfilm, hard copy, optical masks, and stripouuapplications using adhesive materials. Alternative embodiments of this concept are further described in the above cited copending applications.

In a related imaging system described in copending U.S. Patent Application Ser. No. 483,675, filed Aug. 30, I965, now U.S. Pat. No. 3,656,990 nonphotosensitive particulate material is used to form images in the migration imaging mode already defined above. In this system, a developable image is formed by charging in image configuration through the use of a mask or stencil. This image is then developed in a solvent for the softenable material.

There are basically two types of the structures used to form migration images. The first comprises a layered configuration consisting of a conductive or insulating base, and a thin plastic layer which contains submicron size photoconductive particles in an approximate monolayer near the plastic upper surface; and second, a binder structure which differentiates from the layered configuration only in that the submicron size particles are dispersed substantially uniformly throughout the plastic.

All migration imaging processes such as those set forth in the above copending applications begin with the steps of forming a migration image which consists of particles migrated to locations imagewise in depth in the plastic or softenable media. This image is either the final optical image or it is selectively converted to improve its optical character. As defined above, the formation of a migration image results from the development of a latent image by softening the plastic usually by holding the structure for a few seconds in a chamber of solvent vapors or by exposure to a few seconds of heating such as with hot air. Because of the resultant slight dispersion in depth following development of the partially migrated particles, migration images with these particles are visible images, in which the dispersed areas appear less dense or a different color.

The extent to which particle migration occurs is dependent upon a number of variables such as the materials making up the structure; the type of solvent its concentration and time of exposure; or when heat is used, the temperature and time of heating. It can thus be seen that there are a number of variables which must be accurately controlled in order to achieve the desired degree of particle migration in order that the final image be satisfactory in quality in having a minimum or low background.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide a novel method of controlling the formation ofa migration image.

It is a further object of this invention to provide a novel development technique for forming a migration image.

It is yet another object of this invention to provide a novel migration imaging system.

The following objects and others are accomplished in accordance with this invention by providing an imaging system in which a uniform flash exposure of activating radiation such as actinic light is utilized to control development of a migration imaging film. The application or use of a uniform flash or exposure to a suitable source of radiation such as light is used at a predetermined step in the vapor or heat development of a migration imaging film in order to extend the operating voltage range, more accurately control particle migration, and to modify the photographic characteristics of the migration imaging film.

The invention comprises imaging a migration imaging structure comprising a softenable plastic layer contained on a conductive substrate and having at its exposed upper surface photosensitive particles arranged in a particulate layer. The structure in imaged by uniformly electrostatically charging to a given potential, selectively exposing to radiation to form a latent developable image, and developing said image in a solvent for said softenable material, and at some point during the developing cycle uniformly exposing the imaging film to a source of light or radiation which terminates the migration of the particles which otherwise would have continued their migration. The uniform flash exposure may be triggered as soon as the particles have migrated imagewise to or toward the substrate to whatever position is desired. The effect of the exposure terminates particle migration immediately in both the imaged and non-imaged areas. Through the use of this technique. particle migration may be more accurately terminated, hence modifying the photographic characteristics of the film. The action of the flash exposure during development is believed to cause injection of charge by the particles, and thus a loss of their coulombic migration force, and hence terminates migration of the particles within the softenable plastic.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages of this migration imaging system will become apparent upon consideration of the following disclosure of the invention; especially when taken in conjunction with the accompanying drawings wherein:

FIG. 1 shows one embodiment of a typical migration imaging structure.

FIG. 2 shows electrostatically charging the structure of FIG. 1.

FIG. 3 shows exposing the charged plate to form a latent image.

FIG. 4 shows development by exposure to a solvent vapor.

FIG. 5 illustrates flash exposure during development.

FIG. 6 illustrates a second embodiment of exposure during development.

Referring to FIG. 1, there is shown a schematic drawing of an example of one embodiment of this invention comprising an imaging plate 10 having a conductive substrate 11, overcoated with a softenable material 12 which contains at its upper surface a particulate layer of photosensitive material 13.

The conductive substrate 11 may comprise any suitable electrical conductor. Typical substrates are copper, brass, aluminum, steel, cadmium, silver and gold. The substrate may be in any form such as a metallic strip, sheet, coil, cylinder, drum or the like. If desired, the conductive substrate may be coated on an insulator such as paper, glass or a plastic. One example of this type of substrate comprises NESA glass, which is a partially transparent tin oxide coated glass available from Pittsburgh Plate Glass Company. Another typical substrate comprises aluminized Mylar which is made up of a Mylar polyester film of the E. l. duPont de Nemours Company, Inc. having a thin semi-transparent aluminum coating. Another typical substrate comprises Mylar coated with copper iodide.

A dielectric or non conductive substrate may also be used. This may be accomplished by placing the dielectric substrate in contact with a conductive member and charging with a corona charging device as illustrated in FIG. 2. Alternatively, other methods known in the art of xerography for charging xerographic plates having insulating backings may be applied. For example, the plate of FIG. I may be moved between two corona charging devices and raised to opposite potentials to cause the desired charging to be effected. The applied charging potentials for the structures of this invention range from a few volts per micron to several hundred volts per micron of softenable plastic layer 12.

The softenable plastic layer l2 may be any suitable material which is softened in a vapor solvent, or heat, and in addition, is substantially electrically insulating during the imaging and developing cycle. Classes of materials falling within this definition include polystyrene, alkyd substituted polystyrenes, polyolefins, styrene-acrylate copolymers, styrene-olefin copolymers,

silicone resins, phenolic resins, and organic amorphous glasses. Typical materials are Staybelite Ester ID, a partially hydrogenated rosin ester, Foral Ester, a hydroge nated rosin triester, and Neolyne 23, an alkyd resin, all from Hercules Powder Company, SR 82, SR 84, silicone resins, both obtained from General Electric Corporation', Sucrose Benzoate, Eastman Chemical; Vel sicol X-37, a polystyrene-olefin copolymer from Velsicol Chemical Corporation; Hydrogenated Piccopale 100, a highly branched polyolefin, HP-l00, hydrogenated Piccopale I00, Piccotex I00, a copolymer of methyl styrene and vinyl toluene, Piccolastic A-75, I00 and 125, all polystyrenes, Piccodiene 2215, a polystyrene-olefin copolymer, all from Pennsylvania Industrial Chemical Company, Araldite 6060 and 607l, epoxy resins of Ciba; Amoco 18, a poly alpha-methylstyrene from Amoco Chemical Corporation; ET-693, and Amberol ST, phenol-formaldehyde resins, ethyl cellulose, and Dow C4, a methylphenylsilicone, all from Dow Chemical; M-l40, a custom synthesized styrene-co-n butylmethacrylate; R506IA, a phenylmethyl silicone resin, from Dow Corning; Epon l00l, a bisphenol A- epichlohydrin epoxy resin, from Shell Chemical Corporation; and PS-Z, PS-3, both polystyrenes, and ET-693, a phenol-formaldehyde resin, from Dow Chemical, and a custom synthesized /20 mole per cent copolymer of styrene and hexylmethacrylate having an intrinsic viscosity of 0.l79 dl/gm.

In general, the softenable or soluble layer should be from about one-half to [6 microns in thickness, and may be prepared by any suitable technique. Typical methods of preparation include clip coating, roll coating, draw coating, or pour coating; with better control and more uniform results being obtained with dip and roll coating techniques. If the softenable layer is thicker than about 16 microns the photosensitive particles have difficulty in migrating to the substrate, and result in-non-uniform images having poor resolution. Thicknesses below one-half micron do not allow a sufficient depth for particle migration imaging. Thicker layers generally requiring a greater potential for charging, and in general, a thickness from about I to 5 microns has been found to yield particularly good results,

The above group of materials is not intended to be limiting, but merely illustrative of materials suitable for the softenable plastic layer.

The material comprising layer 13 may consist of any suitable inorganic or organic photosensitive material. Typical inorganic materials are vitreous selenium, vitreous selenium alloyed with arsenic, tellurium, antimony or bismuth, etc.; cadmium sulfide, zinc oxide, cadmium sulfoselenide, and many others. U.S. Pat. No. 3,121,006 to Middleton et al. sets forth a whole host of typical inorganic pigments. Typical organic materials are: Watchung Red B, a barium salt of 1-(4'-methyl-5'- chloro-azobenzene-2'-sulfonic acid)-2-hydrohydroxy- 3-napthoic acid, C.l. No. l5865, available from du- Pont; Indofast double scarlet toner, a Pyranthrone-type pigment available from Harmon Colors; quindo magneta RV-6803, a quinacridone-type pigment available from Harmon Colors; quinacridones, such as Monastral Red B(E. I. duPont), Cyan Blue, GTNF the beta form of copper phthalocyanine, C.I. No. 74160, available from Collway Colors; Monolite Fast Blue G8, the alpha form of metal-free phthalocyanine, C.I. No. 74100, available from Arnold Hoffman Company; Diane Blue, 3, 3'-methoxy-4,4'-diphenyl-bis(l" azo-2" hydroxy- 3"-napthanilide), C.l. No. 21180, available from Harmon Colors; and Algol G. C., polyvinyl carbazole, I, 2, 5, 6-di(D,D'-diphenyl)-thiazole-anthraquinone, C.I. No. 67300, available from General Dyestuffs. The x form of metal-free phthalocyanine produced by the method set forth in copending application Ser. No. 505,723, filed Oct. 29, 1965 now U.S. Pat. No. 3,357,989. The above list of organic and inorganic photosensitive materials is illustrative of some of the typical materials, and should not be taken as a complete listing.

The photosensitive particles of layer 13, may be formed by any suitable method. Typical methods include vacuum evaporation; cascading the material while being carried on glass beads or other suitable carrier over the soluble layer 12 which has been softened by a solvent vapor and/or heat; liquid development techniques; powder cloud development techniques; by slurry coating techniques; or by simply dusting the particles of photosensitive material over the slightly softened soluble material.

In addition to the configuration shown in HO. 1, additional modifications in the layered structure are also included within the scope of this invention. One such modification includes an overcoated layered structure in which a layer of photosensitive particles is sandwiched between two or more layers of the softenable material which overlay the conductive substrate. Another configuration includes a binder structure in which the photosensitive particles are dispersed throughout the softenable plastic layer.

The thickness of the particulate layer and size of the photoconductive particles is usually less than about one micron, with the particle size ranging from about 0.01 to 2.0 microns. Particles, larger than about 2.0 microns, do not yield optimum resolution and also show a reduction in image density compared to images having particles less than about 2.0 microns.

The structure or plate of FIG. I may be imaged by uniformly electrostatically charging the surface with a corona charging unit 14 such as illustrated in FIG. 2. The charged plate is then exposed to a pattern of activating radiation such as light 15 shown in FIG. 3. The pattern of imaging radiation 15 is illustrated by a graded pattern of light with a greater exposure occuring in the central portion of the plate as illustrated in FIG. 3. Other methods of forming a developable latent image may also be employed. These include corona charging in image configuration through a mask or stencil, charging with a shaped electrode, or with a pin matrix.

As seen in FIG. 4, the development of the charged migration imaging structure by contact with a vapor solvent 16 results in the selective migration of photosensitive particles in the areas which have been struck by more light ahead of those struck with less light.

The developer solvent 16, may consist of any suitable vapor in which the softenable soluble layer dissolves,

while leaving unaffected the photosensitive material in the form of the original image. The only requirement of the solvent is that it be a solvent for the softenable layer only, and that it be substantially electrically insulating in the sense that the plastic layer 12 is not discharged electrically before migration image formation is complete. The maximum time of exposure to the solvent is in no way critical, inasmuch as the substrate and photosensitive material are selected so as to be substantially insoluble during development. In general, a few seconds of exposure to vapors of the solvent is more than sufficient to soften or dissolve the softenable plastic. Typical solvents are Freon TMC, available from du- Pont; trichloroethylene, chloroform, ethyl ether, xylene, dioxane, benzene, toluene, cyclohexane, l,l,ltrichloroethane, pentane, n-heptane, Odorless Solvent 3440 (Sohio), Freon 113, available from duPont; mxylene, carbon tetrachloride, thiophene, diphenyl ether, p-cymene, cis-2,2-dichloroethylene, octanol, ethyl acetate, methyl ethyl ketone, ethylene dichloride, methylene chloride, l,ldichloroethylene, trans 1,2- dichloroethylene, and super naptholite (Buffalo Solvents and Chemicals).

Momentarily after the beginning of the vapor development, the entire film is uniformly flashed by exposure to a source of light 15 as illustrated in FIG. 5. Flash exposure should be about 5 to 3,000 f.c.s. for about 1/1000 seconds to I second during the migration time which ranges from about 1/10 second to 10 sec onds. The flash should be operated from about l/l00 to 10 seconds after the start of the vapor development. As illustrated in FIGS, the flash has been timed so that the migrating particles have reached substantially the substrate while the particles which have been exposed to only background radiation have only migrated to short depth. By timing the flast to act sooner, as is illustrated in FIG. 6, the migration of the particles may be stopped at any point such as mid-way between the upper surface and substrate softenable plastic interface.

In order to insure accurate control, the use of timers, and/or photocell devices to monitor the formation of the migration image by controlled light exposure may be employed during development.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples specifically define the present invention with respect to a method ofdeveloping an image on a sheet of migration imaging material in which uniform flash exposure is carried out during the developing step. The parts and percentages in the disclosure, examples, and claims are by weight unless otherwise indicated. The examples below are intended to illustrate the various preferred embodiments of imaging a migration imaging structure in which the migration of the photosensitive particles is carefully controlled and terminated at the desired time.

EXAMPLE I An imaging plate or film such as that illustrated in FIG. 1 is prepared by first making a mixture of 20 percent by weight of Staybelite Ester 10 (a 50 per cent hydrogenated glycerol rosin ester of the Hercules Powder Company), dissolved in a solution of toluene. Using a gravure roller, the mixture is then roll coated onto a 3 mil Mylar polyester film (E. I. duPont de Nemours Company, lnc.) having a thin semi-transparent aluminum coating. The coating is applied so that when air dried for about 2 hours to allow for evaporation of the toluene, an imaging plate comprising a two micron layer of Staybelite Ester is formed on the aluminized Mylar. A thin layer of particulate vitreous selenium approximately 0.5 microns in thickness is then deposited onto the Staybelite surface by vacuum deposition utilizing the process set forth in copending patent application Ser. No. 423,l67, filed on Jan. 4, 1965 now aban doned.

EXAMPLE ll An imaging plate or film is formed by the method of Example I in which the Staybelite Ester is replaced with a 20 per cent mixture of an 80/20 mole per cent copolymer of styrene and hexylmethacrylate, dissolved in toluene. The resultant plate comprises a thin particulate vitreous selenium layer approximately 0.5 microns in thickness deposited in the upper surface of the plastic which is contained on a 3 mil aluminized Mylar substrate.

EXAMPLE III A strip of aluminized Mylar consisting of a 75 micron layer of Mylar overcoated with a submicron layer of aluminum, which has a 2 micron rolLcoated overlayer of a softenable plastic Staybelite l thereon, is fixed to the bottom of a rectangular 2 by 6 by 4 inch brass container. The container is rotated about its horizontal axis and cascaded with a developer" mixture of 0.12 grams of Florence Green Seal zinc oxide particles dyed with 0.03 grams of Rhodamine B per 8 grams of zinc oxide, and 50 grams of 50 micron diameter glass beads. The developer material" consisting of carrier beads and zinc oxide particles, is cascaded over the aluminized Mylar strip held to the bottom of the container for l0 rotations or cascades. The strip is removed from the container and heated to 80C. for 2 minutes, refixed in the container, and cascaded again. This cycle is repeated 6 times after which a zinc oxide layer has been formed with the zinc oxide particles dispersed approximately half way through the upper thickness of the softenable Staybelite plastic.

EXAMPLE IV The imaging film formed by the method of Example I is imaged as follows: The film is uniformly charged with a corona charging device such as that described by Carlson in US. Pat. No. 2,588,699 to a positive potential of about 70 volts. The charged film is then exposed to an optical image with the energy in the illuminated areas of about foot-candle-seconds by means of a tungsten lamp resulting in the formation of a latent image in the unilluminated areas. The latent image is then developed by exposing the film to vapors of cyclohexane resulting in the migration of the photosensitive selenium particles which have been illuminated within the softened plastic toward the substrate. About 1 second after the exposure to the solvent vapors, the film is uniformly exposed to a flash of about 3,000 f.c.s. for about one-half second. The vapor treatment is completed in a total time of about 3 seconds. The uniform flash exposure terminates particle migration immediately in both the imaged (exposed) and non-imaged areas.

EXAMPLE V The imaging film formed by the method of Example ll is imaged by the method of Example [V to form a migration image having controlled particle migration.

EXAMPLE VI The imaging film formed by the method of Example [II is imaged by the method of Example IV using a negative voltage of about volts. A migration image having controlled particle migration is formed by this tech nique.

EXAMPLE Vll EXAMPLE Vlll An imaging film prepared by the method of Example H is imaged by the method of Example Vll with the additional step of flash exposure one-half second after the beginning of the vapor development. The flash intensity is 6,000 foot-candles with a duration of from onehalf to 9% seconds. in comparison with the image of Example Vll, which is an image produced without flash exposure, the image obtained in Example Vlll has improved contrast, and attenuation of film sensitivity by a factor of IO, so that the orange area is now at 1 footcandle-second, the light blue area at 4 foot-candleseconds, and the dark blue area at l0 foot-candleseconds. Thus through the use of flash exposure, the control of particle migration results in a control of film sensitivity after the formation of the latent image. In addition, the development time has been significantly decreased.

EXAMPLE [X An imaging film comprising a 4 micron binder layer of submicron size particles of x-phthalocyanine dispersed in the plastic Piccotex I00 contained on a 3 mil Mylar polyester substrate of the type described in copending Application Ser. No. 634,757, now abandoned, filed on Apr. 28, 1967, is imaged as follows: The film is charged to a positive potential of 4,000 volts using a corotron and a conductive backing plate, and exposed through a positive transparency for one-half foot-candle-second. The film is then exposed for 2 seconds to vapors to trichloroethylene. A flash exposure of 500 foot-candles for 1/10 second is made one-half second after the film is exposed to the vapor. After development in vapor, the film bearing the migration image is immersed in trichloroethylene liquid for 2 seconds whereupon the imaging particles remain on the substrate in the unexposed areas only. The liquid development functions to remove the Piccotex binder and unmigrated photosensitive particles in order that thel migrated image contained on the substrate is made visible.

It should also be understood that the instant invention may also be employed in conjunction with imaging structures having non-photosensitive particles contained in a photosensitive softenable layer supported on a substrate. Structures included within this class are disclosed in copending application Ser. No. 553,837, filed on May 31, I966 now abandoned.

Although specific components and proportions have been stated in the above description of the preferred embodiment of this invention, other suitable materials and procedures such as those listed above may be used with similar results. In addition, other materials and changes may be utilized which synergize, enhance, or otherwise modify applicants novel imaging method.

Other modifications and ramifications of the present invention would appear to those skilled in the art upon reading this disclosure. These are intended to be within the scope of this invention.

What is claimed is:

l. A method of imaging which comprises:

a. providing an imaging structure including a support and an overlayer of substantially electrically insulating softenable material containing a particulate material at least one of which is electrically photosensitive, said softenable material capable of having its resistance of migration of said particulate material decreased sufficiently to allow migration of the particulate material through the softenable material toward said substrate,

. forming a latent charge image on said structure,

. developing said latent image by decreasing the resistance of the softenable material to migration of the particulate material at least sufficient to allow migration in depth of the particulate material toward the support with the depth of migration differing between particulate material inside and outside the latent image whereby an image is formed by the selective migration of particulate material in image configuration; and

d. uniformly exposing said member at a time subsequent to the beginning of migration of said particulate material during said developing step but before all the migrating particulate material migrates to the support to actinic electromagnetic radiation of at least about 5 to about 3,000 foot-candle-seconds for at least about 1/1000 second to about 1 second thereby terminating the migration of the particulate material.

2. The method of claim 1 wherein development is carried out by exposing the imaging member to solvent vapors sufficiently to soften the softenable material to allow migration of the particulate material.

3. The method of claim 1 wherein development is carried out by heating the imaging member in an amount sufficient to soften the softenable material sufficiently to allow migration of the particulate material.

4. The method of claim 1 in which the latent image is formed by uniformly electrostatically charging, followed by exposure to a pattern of light.

5. The method of claim 1 wherein said softenable layer is from about one-half to 16 microns thick.

6. The method of claim 1 wherein the size of particulate material is from about 0.01 to 2.0 microns.

7. The method of claim I wherein said particulate material is electrically photosensitive.

8. The method of claim 7 in which the electrically photosensitive material is present in substantially a uniform layer at the upper exposed surface of said softenable layer.

9. The method of claim 7 in which the electrically photosensitive material is dispersed throughout the softenable layer.

10. The method of claim 1 wherein said softenable material is electrically photosensitive.

11. The method of claim I wherein said developing step includes exposing the structure to an electrically insulating solvent which dissolves away the softenable material.

* 'i l l= 

1. A METHOD OF IMAGING WHICH COMPRISES: A. PROVIDING AN IMAGING STRUCTURE INCLUDING A SUPPORT AND AN OVERLAYER OF SUBSTANTIALLY ELECTRICALLY INSULATING SOFTENABLE MATERIAL CONTAINING A PARTICULATE MATERIAL AT LEAST ONE OF WHICH IS ELECTRICALLY PHOTOSENSITIVE, SAID SOFTENABLE MATERIAL CAPABLE OF HAVING ITS RESISTANCE OF MIGRATION OF SAID PARTICULATE MATERIAL DECREASED SUFFICIENTLY TO ALLOW MIGRATION OF THE PARTICULATE MATERIAL THROUGH THE SOFTENABLE MATERIAL TOWARD SAID SUBSTRATE, B. FORMING A LATENT CHARGE IMAGE ON SAID STRUCTURE, C. DEVELOPING SAID LATENT IMAGE BY DECREASING THE RESISTANCE OF THE SOFTENABLE MATERIAL TO MIGRATION OF THE PARTICULATE MATERIAL AT LEAST SUFFICIENT TO ALLOW MIGRATION IN DEPTH OF THE PARTICULATE MATERIAL TOWARD THE SUPPORT WITH THE DEPTH OF MIGRATION DIFFERING BETWEEN PARTICULATE MATERIAL INSIDE AND OUTSIDE THE LATENT IMAGE WHEREBY AN IMAGE IS FORMED BY THE SELECTIVE MIGRATION OF PARTICULATE MATERIAL IN IMAGE CONFIGURATION, AND D. UNIFORMLY EXPOSING SAID MEMBER AT A TIME SUBSEQUENT TO THE BEGINNING OF MIGRATION OF SAID PARTICULATE MATERIAL DURING SAID DEVELOPING STEP BUT BEFORE ALL THE MIGRATING PARTICULATE MATERIAL MIGRATES TO THE SUPPORT TO ACTINIC ELECTROMAGNETIC RADIATION OF AT LEAST ABOUT 5 TO ABOUT 3,000 FOOT-CANDLE-SECONDS FOR AT LEAST ABOUT 1/1000 SECOND TO ABOUT 1 SECOND THEREBY TERMINATING THE MIGRATION OF THE PARTICULATE MATERIAL.
 2. The method of claim 1 wherein development is carried out by exposing the imaging member to solvent vapors sufficiently to soften the softenable material to allow migration of the particulate material.
 3. The method of claim 1 wherein development is carried out by heating the imaging member in an amount sufficient to soften the softenable material sufficiently to allow migration of the particulate material.
 4. The method of claim 1 in which the latent image is formed by uniformly electrostatically charging, followed by exposure to a pattern of light.
 5. The method of claim 1 wherein said softenable layer is from about one-half to 16 microns thick.
 6. The method of claim 1 wherein the size of particulate material is from about 0.01 to 2.0 microns.
 7. The method of claim 1 wherein said particulate material is electrically photosensitive.
 8. The method of claim 7 in which the electrically photosensitive materiAl is present in substantially a uniform layer at the upper exposed surface of said softenable layer.
 9. The method of claim 7 in which the electrically photosensitive material is dispersed throughout the softenable layer.
 10. The method of claim 1 wherein said softenable material is electrically photosensitive.
 11. The method of claim 1 wherein said developing step includes exposing the structure to an electrically insulating solvent which dissolves away the softenable material. 